Phylum Platyhelminthes - FlatwormsDorsoventrally flattened bodieswell defined headBodies are solid (acoelomate)gut is the only internal cavityRibbon-shaped, soft-bodiedMany species are parasiticsome are free-living carnivores orscavengersMove via ciliated epithelial cells on lower surface and waves of contractions of body musclesOrgansdigestive system is branched with a single openingpharynx can be extended/retractedinternal enzymatic digestion, diverticula distribute foodEye spots - cells in light sensitive cupsSimple nervous system with 2 ventral nerve cords, simple brainFree living forms possess chemical sensory systems onlobes of headReproductionMost are hermaphroditic with internal fertilization and separateovaries and testesfertilized eggs deposited in cocoons, hatch into miniature adultsCan reproduce asexually by fragmentation and regenerationNo circulatory system, food and oxygen diffuse to tissuesExcretory system is simple -“flame cells” propel fluidsthrough tubules to outside ofbody - primarily for riddingbody of excess waterThree classes of flatwormsClass Turbellaria - free-living flatwormsClass Trematoda - flukesClass Cestoda - tapewormsClass Turbellaria - Turbellarians, free-living flatwormspredators on smaller organisms, and scavengersfound in water and moist habitatsDugesia, the common planarianClass Trematoda - FlukesParasites on other animalsName originates from their shapeLack sensory and locomotive adaptations offree-living formsfeed on host tissue, food taken in throughmouth, resistant to host defensesComplex life cyclesExample: Clonorchis, human liver fluke - Adults live inassociation with liver - Eggs passed in feces - Ingested by snail -transform into swimming larva that leaves snail - Nonciliatedredia give rise to cercariae - Bore into fish, encyst in muscle -Humans eat uncooked fish, flukes migrate to liverExample: Schistosoma blood flukesCauses disease: schistosomiasis“bilharzia” is spreading through thetropicsClass Cestoda - TapewormsHighly specialized parasitesAdults live in the gut of vertebrates attached to intestinal wallBody divided into scolex, neck and reproductive proglottids (strobila)Absorb food through outer body wallProglottids formed continuously fromregion behind scolex at neckHermaphroditic with testes and ovaries in each proglottidEggs toward end mature, become fertilized - may be self-fertilizedEmbryos and proglottids leave host in fecesExample: Taenia saginata,beef tapeworm - a parasiteof humansPhylum Nematoda - RoundwormsInclude nematodes, eelworms and roundwormsAbundant in marine, freshwater and terrestrial habitats - found everywhereMost are microscopic in sizepredators, parasites, and scavengersTrichinella - the cause oftrichinosisPseudocoelomate body plan - No mesoderm associated with the gutBilaterally symmetrical, cylindrical, unsegmented, covered by thickflexible cuticle that is molted periodicallylongitudinal muscles located beneath the epidermis, pull against cuticle and water filled pseudocoel - Results in side-to-side whipping movement - move well through loose soil or tissuesDigestive systemwith piercing stylets,mouth, pharynx,intestine, and anusSexual reproductionusually separatesexes and internalfertilization,fertilized eggs laidMany nematodes parasitize humans - Ascaris, hookworms, pinwormsExample: Trichinella - pig intestinal roundworm Worm lives in small intestine of pig, young encyst in same host Trichinosis can result if humans eat raw or undercooked pork Worms may also infect
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